In the mobile communication standard GSM/EDGE, the base station can select one of eight training sequence codes as the midamble of the downlink transmitted bursts. If the receiving mobile station uses zero intermediate frequency sampling, the channel estimation is sensitive to the DC offset and IQ gain/phase imbalance of the RF transceiver. This letter shows for a common class of channel estimators that the sensitivity depends on the selected training sequence code. This sensitivity can become significant for 8PSK modulation.